Unstable geomorphologic fabric impacted by excess magmas and propagating rifts in the central West Philippine Basin

The central West Philippine Basin (WPB) comprises three contrasting geomorphologic provinces, the mantleplume type Benham Rise in west, the volcanic arc-type Kyushu-Palau Ridge (KPR) at the east limit, and the in-between central rift hosting the deepest (-7874 m) rifted seafloor. However, their morphic transit and dynamic interactions remain elusive owing to the insufficiency of relevant data. By incorporating new and previous multibeam bathymetry data fully enveloping the central rift, we synthesized a 3-band, 3-segment seafloor fabric of the central WPB and deduced its formation mechanisms. The bathymetry documents prominent across- and along-axis variations and variable landform assemblages, including: 1) overall trends of abyssal hill lineation swing counter-clockwise from -N100/105E at a distance of 100 km from the fossil rift valley to -N85/95E at a distance of -30/50 km, then clockwise to -N100/140E in the rift valley, which recognizes three irregularly bands (I, II, and III ripping into II) and a rotatory spreading fabric; 2) the rift valley narrows westward from -85 km wide near the KPR to -25 km at Centric Deep, and then fades out to further west, synchronously from magmatic to amagmatic then to failed, indicating a northwestward propagating stirred by the KPR volcanism. Moreover, it is found in the middle segment that three major transform faults bend southwesterly into Southern Band I with their concaves pointing to the Benham Rise. Behaving as pseudo-faults, they are likely triggered by the former magmatism of the Benham Rise. Lying just at the intersection of a relict nodal basin and the western tip of the later PR, the Centric Deep might have resulted from overprinting amagmatic extension on former pullapart. Thus, the geomorphic fabric featuring high spreading instability reflects strong magma-tectonic intervention by excessive magmatism of mantle plume and subduction arc.